Add alert management functionality in backend and frontend

This commit introduces alert management capabilities, including creating, updating, listing, and removing custom SQL-based alerts in the backend. It adds the necessary database migrations, API endpoints, and frontend pages to manage alerts, enabling users to define thresholds and monitor system health effectively.

backend/alembic/versions/0002_alert_definitions.py

@@ -0,0 +1,43 @@
+"""add alert definitions
+
+Revision ID: 0002_alert_definitions
+Revises: 0001_init
+Create Date: 2026-02-12
+"""
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision = "0002_alert_definitions"
+down_revision = "0001_init"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "alert_definitions",
+        sa.Column("id", sa.Integer(), primary_key=True),
+        sa.Column("name", sa.String(length=160), nullable=False),
+        sa.Column("description", sa.Text(), nullable=True),
+        sa.Column("target_id", sa.Integer(), sa.ForeignKey("targets.id", ondelete="CASCADE"), nullable=True),
+        sa.Column("sql_text", sa.Text(), nullable=False),
+        sa.Column("comparison", sa.String(length=10), nullable=False, server_default="gte"),
+        sa.Column("warning_threshold", sa.Float(), nullable=True),
+        sa.Column("alert_threshold", sa.Float(), nullable=False),
+        sa.Column("enabled", sa.Boolean(), nullable=False, server_default=sa.text("true")),
+        sa.Column("created_by_user_id", sa.Integer(), sa.ForeignKey("users.id"), nullable=True),
+        sa.Column("created_at", sa.DateTime(timezone=True), nullable=False, server_default=sa.func.now()),
+        sa.Column("updated_at", sa.DateTime(timezone=True), nullable=False, server_default=sa.func.now()),
+    )
+    op.create_index("ix_alert_definitions_target_id", "alert_definitions", ["target_id"])
+    op.create_index("ix_alert_definitions_created_by_user_id", "alert_definitions", ["created_by_user_id"])
+    op.create_index("ix_alert_definitions_created_at", "alert_definitions", ["created_at"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_alert_definitions_created_at", table_name="alert_definitions")
+    op.drop_index("ix_alert_definitions_created_by_user_id", table_name="alert_definitions")
+    op.drop_index("ix_alert_definitions_target_id", table_name="alert_definitions")
+    op.drop_table("alert_definitions")